1. Field of the Invention
This invention relates generally to a method for making cargo liners and floor mats for vehicles. More particularly, but not by way of limitation, the present invention relates to a thermoforming process for producing cargo liners or floor mats for vehicles which include a channel edge about at least a portion of the perimeter of the liners or mats.
2. Background
Cargo liners for pickup trucks, SUVs, vans, and even automobile trunks are well known in the art, as are floor mats for all types of vehicles. A common method for manufacturing such devices is a plastic thermoforming process, in particular vacuum or pressure forming.
Vacuum forming and pressure forming are well known in the art. Generally, to vacuum form a plastic article, a mold is produced, either as a male likeness of the article over which material will be drawn, or a female likeness of the article into which material will be drawn. The mold is typically drilled with small passageways through which air may pass from the molding surfaces to the backside of the mold. A sheet of plastic is then heated until it becomes extremely pliable. The heated plastic is then placed adjacent the mold and vacuum is applied to the backside of the mold. Air passes through the passageways to create low pressure at the surface of the mold, thereby drawing the heated plastic tight against the mold so that the plastic takes on the shape of the mold. The plastic is then cooled and the molded sheet is lifted off the mold. Alternatively, in some cases, compressed air is applied to the backside of the mold so that the molded plastic is blown off of the mold. In a final step, surplus material is trimmed from the edge of the molded article, typically with a router.
Pressure forming is performed in much the same manner except, compressed air is applied to the heated sheet to press it onto the mold. In a sense, this is the same as the vacuum operation in that relatively high pressure air is on the outside of the plastic sheet and relatively low pressure air is on the mold side of the plastic sheet.
In either operation, water or forced air may be used to expedite cooling of the molded article.
While other methods are applicable to forming cargo liners and floor mats, thermoforming of sheet materials has proven to provide a cost effective method of producing finished product of consistent quality. However, a limitation of thermoforming arises in the subsequent trimming operation to remove surplus material from the perimeter of the article. A trimming guide may be used to guide the router operator in trimming the article. While a guide may work quite well when all of the trimming occurs in a single plane, the guide may become quite complex when trimming complex articles. Furthermore, the trimming operation may introduce some variability into the dimensions of the finished article and it is often difficult to produce a straight edge of consistent width.
Articles formed of relatively soft material may be hand trimmed using a knife. Unfortunately, hand trimming will often leave the trimmed edge of part irregular and the consistency of the operation is dependent on the skill of the individual. In addition, hand trimming places relatively large stresses on the wrists of the individual performing the operation.
Therefore it can be seen that there is a need for a method for making cargo liners and floor mats using a thermoforming process which facilitates trimming of the molded part in a secondary operation.
It is thus an object of the present invention to provide a method for thermoforming a cargo liner or floor mat wherein a channel edge is formed during the molding process to facilitate cutting and to provide an improved article.
The present invention provides a method for making cargo liners and floor mats using a plastic molding process. In the inventive process, a steel rule or a groove is incorporated into the mold to produce a ridge in the molded part to facilitate subsequent trimming.
In a preferred embodiment, when heated plastic is drawn over a steel rule during a thermoforming process, a channel edge is formed in the plastic article about its perimeter. During a subsequent trimming operation to remove surplus material, trimming is performed on the ridge created by the steel rule thereby reducing variations in the edge which result from the trimming operation to produce an edge which enhances the appearance of the finished article with less dependance on operator skill during the trimming operation. An article produced by the inventive process will include a channel edge about at least a portion of its perimeter.
While the inventive process is applicable to virtually any molding operation which requires a subsequent trimming operation, it is especially well suited to thermoforming of plastic sheet materials. By way of example and not limitation, such processes include vacuum forming, pressure forming, and rotational molding. Furthermore, such forming may involve either a male mold or a female mold.
Further objects, features, and advantages of the present invention will be apparent to those skilled in the art upon examining the accompanying drawings and upon reading the following description of the preferred embodiments.